Dr. C. I. Forsyth Major — 8ome Rodents from Oeningen. 371 



therefore a priori not unlikely that the larger forms from Oeningen, 

 comprised generally luider the single denomination ' Lagomys 

 Oeningensis,^ may equally include two different animals. For this 

 reason something more is required than mere measurements, if we 

 wish to determine more satisfactorily these so-called ' Lagomys 

 Oeningensis.^ 



On inspection of the specimen No. 42,815 from Oeningen, several 

 cheek-teeth were detected in a fragment of the cranium examined 

 from their inner side, the bone being broken away ; the lower 

 parts of these teeth were near the crown ; this latter, however, 

 w^as hidden in the matrix when the specimen was placed in 

 my hands. By carefully removing the matrix, the triturating 

 surface of the three anterior cheek-teeth (the three premolars) 

 could be developed, and, as a result, it became at once apparent 

 that the fossil is a JLagopsis. The posterior of the three teeth 

 (p. 1) exhibits the pattern which is shown bj"- the homonymous 

 premolar of Lagomys and by the latter's two true molars. On the 

 outer side of this tooth is a shallow and open groove, which, as far 

 as can be made out with a strong lens, has no enamel border. From 

 the middle of the inner margin a lozenge-shaped narrow fold of 

 enamel runs transversel}'^ across two-thirds of the breadth of the 

 triturating surface, tovyards the outer side ; the posterior enamel 

 bordering of this fold is raised into a strong crest, running 

 parallel with the anterior enamel bordering of the tooth, both 

 presenting a slight anterior convexity. The enamel folding is 

 filled with cementum in its outer narrower portion, its wider 

 internal opening being devoid of this substance. The pattern of the 

 median premolar, p. 2, proves that the isolated tooth from La 

 Grive, before mentioned, has been rightly determined as p. 2. 

 There is only a comparatively shallow internal enamel folding 

 present in this tooth (a, Fig. 1) ; the greater part of the triturating 

 surface being occupied by the enamel crescent [h, Fig. 1) before 

 described in the tooth from La Grive. Outside from the crescent 

 appears a small enamel ring (c. Fig. 1) filled with cementum, 

 doubtless the vanishing homologue of the outer enamel crescent c of 

 Titanomys and Prolagus, as elsewhere described and figured. In the 

 La Grive specimen there is a mere vestige of some such element in 

 the same place, the latter tooth being presumably more worn than in 

 the Oeningen specimen. Li the p. 2 of Lagomys the outer enamel 

 bordering of crescent h is raised into a strong triangular cusp, turning 

 its convexity inwards ; in the fossil the inner border of the crescent 

 is raised in the same manner. 



The anterior premolar (p. 3) of the Oeningen fossil is not dis- 

 similar from the same tooth of Prolagus Oeningensis (Kon.), Whereas 

 in recent Lagomys the triturating surface of p. 3 exhibits only one 

 enamel folding, starting from about the middle of the anterior 

 margin and running backwards obliquely, i.e. postero-externally, 

 the same tooth in our Lngopsis shows, as in Prolagus Oeningensis, 

 two enamel foldings, opening on the anterior margin and thence 

 runnin"; almost straia:ht backwards. 



